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Old 13th February 2010, 11:09 PM   #21
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You'd have to remove it from the circuit to determine if the diode is defective or if something in parallel with it is causing it to appear defective.
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Old 14th February 2010, 04:13 AM   #22
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Perry,

I have 1 of theese amps of my own. Amp works pefect never been worked on.

If you need any info on this amp let me know
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Old 14th February 2010, 03:42 PM   #23
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I appreciate it but one slip of the probe could cause $100+ in blown parts. I wouldn't want you to risk that.
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Old 16th February 2010, 01:44 PM   #24
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Ok after looking over the circuit for a bit I was able to trace both pins 13 and 15 back to the same points. They lead down to the main board via a pin (Vgs). After which the trace leads to a bank of 4 transistors right beside the power supply FETs.

The trace seems to connect to the center leg of 2 of the transistors (C1027). I assume these are the driver transistors?

Could these have failed and need to be replaced?

Thanks
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Old 16th February 2010, 03:43 PM   #25
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These go to the collectors of the NPN driver transistors. The NPN drivers and the board simply use the same voltage source. You need to follow the circuit back a bit farther to find the source of the voltage.
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Old 17th February 2010, 11:20 PM   #26
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Ok I looked over it again and found that pins 13 and 15 are also connected to a transistor on the far left side of the driver board. This transistor (C1027) looks like it has been replaced in the past due to its solder joints. This transistor is indicated with the red circle on the attached photo.

The initial path of the 12v B+ circuit is indicated by the yellow lines.

The picture might have to be enlarged to see the drawings

Click the image to open in full size.

could this transistor be the issue?
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Old 17th February 2010, 11:32 PM   #27
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With the amp powered up, the meter set to DC volts and the black probe on the chassis ground terminal, what is the voltage on the 3 legs of that transistor?


Leg 1:
Leg 2:
Leg 3:
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Old 17th February 2010, 11:45 PM   #28
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reading from the outside leg (closest to the big resistor) in = 7.8V,9.5V,8.5V
The speaker relay was going crazy the whole time as well.

also I accidentally touched the outside leg of the transistor and the big resistor with the probe at the same time, and voila green power light. So I assume the problem is to be found in this transistor or no?
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Old 17th February 2010, 11:54 PM   #29
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If the voltage was taken looking at the marked side of the transistor and they're taken left to right, the transistor appear to be OK. The voltage on its base makes it appear as if it's being used as a regulator. Does the 3rd leg go to the diode on the edge of the board?
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Old 18th February 2010, 12:15 AM   #30
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It seems as if the 3rd leg does lead to the red-ish diode on the edge of the board by the speaker terminals. I had to leave the amp in a different location, but I am going of the picture I have of the board.

I was happy to see the power light turn on earlier but didn't want to leave those parts shorted for fear of damage.
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